438
STEPHENSON’S PATENT
for five inches in length, having a collar at the end; these parts, G G, turn in
brasses, which are fixed in the outside frame of FlG * 22,
the engine, and have the weight of the engine
resting upon them. The axle is all turned in
a lathe, and each of the crank pins is also
turned by suspending the axle on centres cor
responding with the centre of the crank pins;
and made in strong cast iron arms, that are
firmly fixed on the ends of the axle, and pro
ject beyond the cranks, so as to balance the
axle, and enable it to turn round on the centre
line of the crank pin. The axle is by this means
made very true, and the cranks are made of
exactly the proper length, and at right angles to
each other. The corners of the cranks are
champered off, as shewn in the figure, and the
ends of the smaller cylindrical parts well
rounded out.
The crank R of the right hand cylinder
is shewn vertically, and in its lowest position;
and the piston in the cylinder is shewn in the
middle of its stroke, or at half stroke. (See
Plate XC.) If the piston be now made to
move backwards, by admitting the steam to
the front of it, it will press against the crank
pin by means of the piston rod and connecting
rod, with a force equal to the pressure of the
steam upon it; and as the piston is twelve inches
diameter, or 113 square inches area, this force
upon the crank will be 2^ tons, when the
steam is at the usual pressure of 50 lbs. per
square inch. And as the cylinder and cranked
axle are firmly connected together by the frame- Fig . 2 3.
work of the engine, they cannot be sejmrated by this force upon the crank;
the crank therefore gives way by turning round, making the axle and wheels
upon it revolve in the direction of the arrow, until it is brought to its farthest
position and becomes horizontal, as the left hand cylinder is shewn in Plates XC.
and XCI., and the piston has arrived at the end of its stroke.